In known mining equipment for the underground mining of coal or other mineral products, the working face side of a scraper chain conveyor is often fitted with lateral chain guides in which is guided a driven chain with which a mining machine, e.g. a plough, is moved along the scraper chain conveyor. In the usual coal plough installations the chain guide at the same time forms a guide for the plough. In general, the plough guide has two such chain channels situated one above the other, of which one chain channel, usually the lower one, has an aperture in the form of a slot, through which the plough passes. The plough is then affixed to the center of the plough chain by means of guide blocks.
In practice, the plough chain is drawn or retracted into the lower channel of the plough guide from time to time by means of a suitable mechanism e.g. for assembly to the plough. A known mechanism has a retraction slide which can be inserted from the outside through the slot of the plough guide into the lower channel of the latter and to which the chain to be drawn through the channel is affixed by its end. In this system, the retraction slide is connected, outside the plough guide, to a traction member, e.g. a traction chain, provided at its other end with a so-called chain claw, i.e. a coupling piece, by the aid of which the mechanism can be connected to a scraper chain assembly of the scraper chain conveyor, so that with the aid of the driven scraper chain assembly the retraction slide and thus the plough chain coupled to it can be drawn through the chain channel of the plough guide. The mechanism thus serves as an aid to the assembly by drawing the plough chain into the particular chain channel to which access from the outside is difficult, if not impossible, when the plough guide is attached.
If one or more chain pieces are used for the traction member they usually consist of heavy oval-link chain sections, and overloads may develop particularly on the chain claw and the retraction slide, when blockages occur during the displacement of the drive chain, e.g. when the retraction slide tilts or jams. This may cause serious damage to the constructional parts, as the mechanism is in a drive connection with the scraper chain assembly of the scraper chain conveyor and the latter cannot be immediately brought to a stop. Breakages of the mechanism, moreover, present a serious danger to the coal face workers.
An object of the invention is to provide an improved mechanism or gear of the aforementioned kind in which drawing of the drive chain is not accompanied by any serious risk of danger to personnel or damage to equipment.